The present invention relates to a displacement control valve configured to be used in a variable displacement compressor. In the variable displacement compressor, refrigerant is supplied from a discharge pressure zone to a control pressure chamber through a supply passage and sent out from the control pressure chamber to a suction pressure zone through an outlet passage. In this manner, the pressure in the control pressure chamber is adjusted to control displacement of the compressor.
Such variable displacement compressors include a control pressure chamber accommodating a swash plate having a variable inclination angle. Specifically, the inclination angle of the swash plate decreases as the pressure in the control pressure chamber increases. The inclination angle increases as the pressure in the control pressure chamber decreases. A decrease in the inclination of the swash plate leads to a decreases in the piston stroke, thus decreasing displacement of the compressor. In contrast, an increase in the inclination angle of the swash plate causes an increase in the piston stroke so that the compressor displacement increases.
The pressure in the control pressure chamber is adjusted using, for example, a displacement control valve disclosed in Japanese Laid-Open Patent Publication No. 11-280660. The displacement control valve includes a first valve mechanism for adjusting the opening degree of a passage extending from a crank chamber to a suction chamber in correspondence with extension/contraction of a bellows sensing the pressure in the suction chamber or the crank chamber. The displacement control valve also has a second valve mechanism for adjusting the opening degree of a passage extending from a discharge chamber to the crank chamber in correspondence with opening/closing of the first valve mechanism. The second valve mechanism receives the pressure in the crank chamber or the suction chamber on the surface of a second valve body opposite to the surface of the second valve body by which the second valve body contacts a valve seat. In the second valve mechanism, the pressure receiving area of each of the opposite surfaces of the second valve body is adjusted to substantially cancel the influence by the pressure in the discharge chamber in the directions in which the second valve body is selectively opened and closed. An urging spring is arranged between a valve casing receiving the bellows and the bellows. The urging spring urges the bellows in the direction in which the first valve mechanism closes.
To prevent the second valve mechanism from being influenced by the discharge pressure, the displacement control valve applies the pressure in the crank chamber or the suction chamber also to the back pressure portion of the second valve body. Also, the displacement control valve adjusts the discharge pressure through the valve body so that the displacement control valve as a whole does not receive the discharge pressure. Further, the bellows is urged by the spring to maintain the first valve body in a closed state even when the pressure in the suction chamber increases and the bellows contracts. In addition, since the second valve body is maintained in an open state, a minimum displacement is maintained constantly even when the electric current value in the electromagnetic solenoid is zero.
The bellows is urged by the urging spring such that the first valve body is urged toward a valve hole closing position. The urging force of the urging spring is set to such a value that the first valve body is maintained in the closed state even if the pressure in the suction chamber increases and the bellows contracts. Accordingly, when the first valve body is urged to open by the electromagnetic solenoid, an electric current must be supplied to the electromagnetic solenoid by an amount corresponding to the urging force of the urging spring. Also, when the pressure in the crank chamber increases at the minimum displacement at which the first valve body is maintained in the closed state, a guide is urged by the pressure in the crank chamber to open the first valve body. If the urging force of the urging spring is small compared to the pressure in the crank chamber, the first valve body opens.
As has been described, the conventional configuration allows the first valve body to open when the pressure in the crank chamber increases at the minimum displacement, at which the first valve body is maintained in the closed state. As a result, the minimum displacement cannot be maintained, and the power consumption of the compressor cannot be reduced.